Prior to the advent of the metal connector in the late 1800's, structual wood members were commonly joined by a method known as toe nailing. In this method, a practice which is still being carried on, a wood joist for example is connected directly to a beam by driving nails at an angle through the joist and into the beam. Toe nailing frequently results in splitting the end of the joist member which can result in premature failure of the structure. There are two main reasons why toe nailing splits the end of the wood joist member. First, if the workman nails the joist too close to the joist end or causes the nail to penetrate the joist end at too shallow an angle, the joist end will split immediately. Second, even if the joist is correctly toe nailed, the joint is inherently weak since a load on the joist member sufficient to cause bending of the nails acts like a wedge in the joist end thereby initiating splitting. As a consequence of the inherently weak joint when toe nailing is used, building codes assign a low load carrying ability to toe nailed joints. In standard toe nailing the nails are all in single shear. Because toe nailing frequently results in splitting the end of the joist causing a weakening of the member and toe nailing is limited by the relatively low support value, workers in the art sought to provide metal connectors.
One of the earliest hangers known to applicant is Van Dorn, U.S. Pat. No. 537,505, a wrought metal joist hanger patented in 1895. The Van Dorn hanger is formed with header sides and top flanges which are nailed to the supporting header wood member and a seat for carrying the supported member; a design which has not changed in concept to the present time. The Van Dorn hanger was a radical departure from the accepted practice of the day since it entirely eliminated toe nailing and the consequent end splitting problem. Note that none of the fasteners penetrated both the held member and the holding member, and all nails remained in single shear.
Van Dorn was followed by Eberhardt, U.S. Pat. No. 753,053, who received a patent in 1904 for his sheet metal joist hanger which relied solely on a top flange to connect the hanger to the supporting wood member. A seat, as in Van Dorn, carried the supported member and, again, all toe nailing was eliminated. All the nails remained, however, in single shear.
In spite of the relatively early invention of sheet metal hangers, they did not come into wide usage until the 1940's when mass production of homes clearly demonstrated the superiority of using metal hangers. Several types of metal hangers and connectors were adopted and used and all of them avoided the problem of end splitting caused by toe nailing by never allowing any nails to penetrate both the held and holding members. Further, all of the previous metal hangers position the nail fasteners so that the nails are always in single shear.
Applicants have found only two connectors which are configured to permit toe nailing as well as standard single shear nailing.
In 1910, Hulett, U.S. Pat. No. 949,075 taught a porch hand rail support which had a seat for carrying the rail and a back wall with a large opening so that one or more nails could be driven through the top of the hand rail through the large opening in the metal bracket and thence into the post. No interlocking between the toe nails and the metal bracket occurred and all the nails remained in single shear. In 1962, Findleton obtained U.S. Pat. No. 3,036,347 for a joist hanger having the usual top flange for connection to the supporting member and a seat for carrying the supported member. Findleton's contribution to the art was a choice of two methods to prevent overturning of the supported member in the hanger. One of the methods was to provide a large hole in the back of the hanger like the Hulett bracket and permit the driving of a toe nail through the top of the supported member, through the large opening in the hanger and into the supporting beam. Again, the toe nail made no interlocking connection with the hanger itself and all the nails remained in single shear. While the toe nail provided some direct support for the joist member, most of the load was carried by the seat member of the hanger. The Findleton hanger, because of its tendency to split the joist end was not commercially adopted and is not known to be in present use.
An example of a joist hanger which is in wide commercial usage at the present time is Gilb, U.S. Pat. No. 3,601,428. This hanger is mass produced by means of progressive die techniques but, again, no toe nailing is provided. Nails in the side flanges are driven only into the supporting member and prongs and nails attach the sides of the metal hanger only to the supported member. Such hangers have no end splitting problem, but all nails are in single shear resulting in limited code load values for each nail resulting in a hanger which requires many nails and extra metal.
As mentioned previously, the practice of toe nailing still persists to this day and some workers in the field have tried to solve the end splitting problem with toe nailing devices such as the one shown in Nelson U.S. Pat. No. 3,147,484, 1964. But, as earlier stated, even with perfect toe nailing, the joint still remains inherently weak.
Two recent patents are relevant to the present invention. They are Gilb, U.S. Pat. No. 4,230,416, 1980, and Gilb, U.S. Pat. No. 4,291,996, 1981. Gilb '416 taught the use of a restricted nail slot opening so that a nail could be driven on a slant. The slot openings are used for skewed angle hangers. No toe nailing is involved and one set of nails connects the back flanges to the supporting member and the other set of nails connects the sides of the hanger to the supported member thus all nails are in single shear.
In Gilb, '996, a positive nail angling device is taught to prevent splitting of laminated wood members such as plywood and prefabricated wood joists (Microlams) by insuring that the nails are driven at an angle into the laminated wood members rather than parallel to the laminations. The positive nail angling device also solves the problem of beam failures due to suspension of the supported member on the side nails after wood shrinkage and subsequent reapplication of large loads on the suspended supported member. Splitting of the supported wood member may occur when the wood member is forced back down on the supporting seat. Gilb, in his '996 patent supra follows the standard hanger practice of carrying the supported member on a hanger seat and providing no toe nailing or direct nail connection between the supported member and the supporting member. All nails are in single shear resulting in the use of many nails and extra metal to provide for the many nail openings.
In the light of the present disclosure, it is now possible to see that, the connectors of the last 87 years were inefficient in that they required far too many nails and used 40 to 50% more metal than the connectors described in this application. Simply stated, the connectors of the past 87 years were designed so that each and every nail used in the hangers was in single shear which can carry a relatively low load value. Further, all of the prior art hangers just supported vertical loads and only nominally prevented "uplift". Recently "uplift" has become a common requirement for seismic and hurricane code requirements. Present hangers require top straps to meet seismic codes. This "band-aid" approach is expensive and generally unsatisfactory.